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Lava flow thickness estimation on the Moon and Mercury based on modeling the topographic degradation of partially buried impact craters

Abstract : In this study, partially buried craters on the lunar maria and the northern smooth plains of Mercury were identified using recently acquired optical, elevation, and composition data, and lava flow thicknesses near partially buried craters were estimated by numerically modeling their topographic degradation. In Chapter 1, I first introduce the geologic background of the volcanic plains on the Moon and Mercury. Next, I will summarize all the methods that have been used to estimate the lava flow thicknesses on the Moon and Mercury, as well as the research progress on the crater topographic degradation. In Chapter 2, I present the remote sensing datasets used in this study. Then, the criteria used to identify partially buried craters are discussed. A lava flow thickness estimation method is later proposed based on the topographic degradation of partially buried craters. The best fitting lava flow thickness was then determined by minimizing the difference between the modeled final profile and the observed profile. In Chapter 3, in order to solve the topographic diffusion equation, the elevation profile of a fresh impact crater is constructed as the initial condition. For lunar fresh impact craters, we constructed a set of topographic profiles that consider both crater sizes and target types. For fresh impact craters on Mercury, we constructed topographic profiles that only include transitional and complex craters. As described in Chapter 4, the basalt thicknesses were inverted using 41 mare craters whose rims are completely exposed. The result shows that the estimated mare basalt thicknesses vary from 33 to 455 m, with a median value of 105 m. We then calculated the total volume and eruption rate of lunar mare basalts, and found that the estimated eruption rate of mare basalts peaked at 3.4 Ga and then decreased with time, indicating a progressive cooling of the lunar interior. We also found that the topographic diffusivity of lunar craters increases with diameter and is almost invariant with time. In Chapter 5, I present a similar result for Mercury. The lava flow thicknesses were inverted for 17 craters whose rims were exposed and embayed for more than 50% of its circumference. The result shows that the lava flow thicknesses vary from 7 to 419 m, with a median value of 218 m. We then calculated the total volume and eruption rate of the lava flows. Comparing the topographic diffusivity on the Moon with that on Mercury, it can be found that both values are similar to each other. As shown in Chapter 6, there are some remaining issues that need to be solved in the future. First, I employed a simple axisymmetric geometry when analytically solving the topographic diffusion equation and did not consider a fully three-dimensional topographic degradation process. Second, the inverted topographic diffusivities have a large range of uncertainty and are not well constrained. Third, complex craters usually have complicated formation mechanism and a variable geologic background and crater morphology, resulting in considerable variability and uncertainty in the crater morphometric relations.
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  • HAL Id : tel-02877812, version 2

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Jun Du. Lava flow thickness estimation on the Moon and Mercury based on modeling the topographic degradation of partially buried impact craters. Astrophysics [astro-ph]. COMUE Université Côte d'Azur (2015 - 2019), 2019. English. ⟨NNT : 2019AZUR4099⟩. ⟨tel-02877812v2⟩

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